This invention relates to electronic calculators and more specifically to the mechanical assembly of the components comprising an electronic calculator.
In prior art, hand-held electronic calculators, the electronic circuitry usually comprises one or more integrated circuits mounted in a plastic or ceramic package with a large number of leads protruding from the sides of the package. Typically, these leads are bent 90.degree. to allow the leads to be inserted in holes in a printed circuit board for soldering in order to make electrical and mechanical connection between the printed circuit board and the integrated circuit.
This commonly used method of assembly has a significant number of drawbacks. When the integrated circuit leads are soldered to the printed circuit board, the integrated circuit is subjected to heat which may damage it and thus reduce the production yield of calculators. Also, in order to insure a good solder joint a flux is usually used to clean the parts and enable the solder to make a good bond between the conductors on the printed circuit board and the integrated circuit package leads. These fluxes are often corrosive and thus must be removed completely after the soldering operation so that gradual deterioration of the contacts will not be caused by any remaining flux. This extra operation, of course, means added cost in the production of the calculator. Occasionally a solder joint will be incomplete so that one lead does not make proper contact with the printed circuit board. On the other hand, solder may flow up through a hole in the printed circuit board, a process known as wicking, and actually short together two leads. Inspection after the soldering operation is typically necessary and some touch up of the assembly is also necessary in order to make sure that all solder joints are good and that there are no shorts. These hand operations naturally add to the cost of assembling a calculator. If upon inspection it is found that an integrated circuit is defective, the entire assembly must either be discarded or the integrated circuit must be removed, typically by manually unsoldering all of the joints, and a new integrated circuit must then be soldered in by hand in its place. This operation makes reworking expensive.
One of the prior methods for solving some of these problems is to provide a socket for the integrated circuit. The socket is soldered into the printed circuit board and the leads of the integrated circuit package are inserted into the socket. These sockets, however, are relatively expensive and still do not prevent the problems of flux corrosion and wicking. In addition, such sockets add bulk and weight to the assembly and space is usually at a premium in hand-held electronic calculators.